In a conventional automatic ice making device, a thermistor furnished to an ice chill tray detects judgment that water has been frozen, and a microcomputer controls an ice discharging operation, as disclosed in, for example, Patent Laid Open No. 2000-292042.
In the following description, with reference to the attached drawings, explanation will be made to the above mentioned conventional ice chill tray.
FIG. 4 is a system-block diagram of the conventional automatic ice making device. In the same, this conventional automatic ice making device is provided with
electric heater 1 furnished to an ice chill tray for separating ice,
AC motor 2 for discharging ice,
solenoid valve 3 for pouring water,
thermistor 4 for detecting temperature of the ice chill tray,
switch 5 for detecting ice of a predetermined amount stored in an ice bucket,
triacs 91 to 93 for controlling electric conduction to heater 1, motor 2 and solenoid valve 3,
microcomputer 6,
gate drive circuit 7 for outputting gate signals of respective triacs 91 to 93,
DC power source circuit 8 of outputting 5V voltage, and
thermal fuse 10 working at overheating of triacs 91 to 93 and the ice chill tray.
The ice chill tray structured as above mentioned will be explained in operation.
Microcomputer 6 reads in output voltage of thermistor 4, and when a detected temperature goes down to, for example, around −5°, it turns ON triac 93 for a determined time (for example, 4 seconds) via gate drive circuit 7. If turning ON triac 93, solenoid valve 3 opens to pour water into ice chill tray 3.
Microcomputer 6 then detects the ice-making, and turns ON triacs 91, 92 via gate drive circuit 7. Electric heater 1 is heated and AC motor 2 is driven.
If pawls of ice discharging mechanism contact ice in company with rotation of AC motor 2, AC motor 2 is locked. After awhile, the temperature of the ice chill tray goes up by electric heater 1, portions of ice contacting the ice chill tray begin melting, and ice separates from the ice chill tray. Ice is discharged from the ice chill tray by rotation of AC motor 2. When the ice-discharge is completed, conduction to electric heater 1 is stopped, and pawls of the ice discharging mechanism are held at a predetermined position. By the above series of operations, one cycle of the ice making work is finished.
However, with the above mentioned mechanism, in case the power supply is interrupted by such as interruption of power supply, and the power supply is recovered immediately after ice in the ice chill tray melts and becomes water, and in spite of still presence of water in the ice chill tray, if the thermistor detects a predetermined temperature, water is further supplied. Water therefore possibly overflows from the ice chill tray.
All of electric heater 1, AC motor 2 and solenoid valve 3 are controlled by the microcomputer, so that the control part will be at high cost.